File Encryption

How to use the file encryption

1. Choose the file to encrypt.
2. Enter a long passphrase, twice.
3. Download the encrypted file and store the passphrase safely.

About this tool

The file is encrypted with AES-256-GCM, and the key comes from your password through PBKDF2 at 310,000 iterations. A random salt and starting vector are generated for every file and stored in its header, so encrypting the same file twice produces two entirely different outputs — that is correct behaviour rather than a fault, and a tool that produced identical output would be leaking information.

The iteration count is written into the file rather than assumed, which means a file encrypted today still opens after the default is raised. The header also identifies the format, so a file that is not one of ours is reported as such instead of failing with something incomprehensible.

The password is the whole of the security, and no amount of key stretching changes that. PBKDF2 makes each guess expensive, but a dictionary word or a short password falls in minutes on rented hardware whatever the iteration count. Use a long passphrase.

There is also no recovery, and that is worth understanding before you rely on it: nothing here keeps the file, the password or a key, so a forgotten password means the data is gone. That is the same property that makes the tool worth using — a service that could recover your file is a service that can read it.

Common uses

• Encrypting a document before sending it through email or chat.
• Protecting a file before putting it in cloud storage.
• Storing something sensitive on a shared machine.

Frequently asked questions

What encryption is used?

AES-256-GCM, with the key derived from your password by PBKDF2 at 310,000 iterations using SHA-256, and a fresh random salt and starting vector for each file.

Why is the encrypted file different each time?

Because the salt and starting vector are random for every encryption. Identical output from identical input would leak the fact that they are identical.

Can the password be recovered?

No. Nothing here stores the file, the password or a key, so a forgotten password means the data is unrecoverable — which is the same property that makes it worth using.